1. Field of the Invention
The present invention relates to a microcomputer. More particularly, the present invention relates to a microcomputer capable of appropriately setting a state such as a state of reset-start according to a state of the electric power source.
2. Description of the Related Art
Microcomputers are widely used for controlling various types of electronic equipment. In general, electric power is supplied to the microcomputer 100 from the electric power circuit 10 provided in the electric equipment as shown in FIG. 6. When the electric power circuit 10 is turned off, the detection circuit 101 housed in the microcomputer 100 detects the occurrence of an abnormal condition of a level of electric power source voltage VDDIN. By the result of detection, the microcomputer 100 conducts the setting of self-status, or the microcomputer 100 conducts the reset-start when the supply of voltage from the electric power source circuit 10 is returned.
In this connection, in the microcomputer 100, the condenser 30 used for backup is attached to its electric power source. The reason why the condenser 30 used for backup is attached to the electric power source is described as follows. When the electric power source circuit 10 is turned off, the level of electric power source voltage VDD is temporarily maintained by the condenser 30 used for backup, so that data stored in RAM and the register housed in the microcomputer 100 can be maintained.
For the above reasons, although the detecting circuit 101 for detecting the level of electric power source VDD is provided, a change in the level of electric power source VDD, which is caused when the electric power source 10 is turned on and off, is small. Therefore, it is difficult to appropriately reset the state of the microcomputer 100 according to the state of the electric power source.